Planet CNC initial setup and limits?

[Neale]

Typically you will have at least one switch per axis that is used for homing. That is, when you first fire up the machine at the start of every session, you "home" all axes. The software moves the axis in the direction of the limit switch; when it trips the software now knows exactly where the hardware is. A better-specified machine might have limit switches at the other end of travel as well that detect if the software tries to drive the axis beyond limits. Without these (and I'm talking Mach3 here although I assume that your motion-control software will do something similar) you can set up soft limits. That is, limits that enforced by the software rather than external hardware. Less reliable, depend on the initial homing being done, etc, but a lot of people will use both - soft limits set just within the hard limit values. Soft limits will often stop you doing something stupid but hard limit switches at both ends are the final belt-and-braces that will stop the machine if it all goes pear-shaped.

Depending on the type of limit switches your machine has, it is probably not difficult to add further limit switches at the other end of X and Y. Usually there is no lower Z axis limit switch as down travel depends a lot on tool length, etc. Z home/limit is usually at the top of travel. Most people probably have the home position at X=0,Y=0, but it is possible (Mach3 again) to set the home position at the other end of travel if that is more convenient. I helped a friend set up his machine where the orientation in the workshop meant that he wanted X=0 to be at the LH end, but the home switch was at the RH end. So we just reconfigured the X home position to be X=900 (or whatever it was).